Compounded lubricant



Patented Dec. 9, 1941 COMPOUNDED LUBRICANT George L. Matheson, Union, N..L, asslgnor to Standard Oil Development Company, a corporation ofDelaware No Drawing.

Application May 8, 1940,

Serial No. 334,012

. amounts, as to have little effect on the fluidity 13 Claims.

This invention relates to lubricating compositions adapted for servicein automotive engines and is particularly concerned with the preparationof Diesel and aircraft lubricants.

Development in the art of preparing lubricants for automotive engines isdetermined largely by the quality of available mineral oils. For thelubrication of these engines, mineral oils alone are oftenunsatisfactory because hydrocarbons do not possess the necessaryproperties under all conditions of engine operation. The incorporationin the higher mineral oil fractions of selected compounds has been foundto enhance the lubricating properties of the oil base and impart to thecomposite properties not possessed by the oil base. Some of theimprovements effected in this manner are in regard to oiliness, filmformation and tenacity, viscosity-temperature relationship, pour point,physical and chemical stability, color and cast characteristics, andfunctioning of the lubricant without fouling of the engine system. Thepresent invention is concerned particularly with the improvement inlubricants in regard to clean engine performance.

Engine cleanliness is concerned largely with the condition of the pistonassemblies, the rings, slits, grooves, lands, skirts and the like, ofcrankcases, valve chambers, filters and oil lines, and the prevention ofthe deposition on these of gummy, varnish-, or sludge-like deposits. Thedeposits may form as a result of the deterioration of the minerallubricating oil, or may be partially or wholly formed from fuelresidues, water and dirt which find their way into the oil. Thedeposits, however, are not to be confused with the gums and resinsdeposited in the engine system by fuels containing, for instance, gumformed by the aging of the hydrocarbons in storage. The fuel depositsare not of the same type or located in the same portions of the enginesystem. Thus, in the case of the fuels, carburetor jets are choked bygummy material and gum and resinous materials are deposited in theinduction system of the engine, as for example on the inlet valve stem,causing the valve to stick in its guide.

In the endeavor to combat the fouling of engine systems many metallicsalts have been investigated. The use of metallic salts for this purposeis not to be confused with the uses of soaps to improve viscosity and asthickening agents. When employed to obviate the fouling of the enginesystem, the metallic salts are necessarily of such a nature, and addedin such of the base oil, otherwise the normaloil circulation system ofthe engine would be unable to handle the lubricant.

The metallic salts appear to owe their effect at least in part to adetergent action which enables the compounded oil to scour from theengine surfaces such sludges and lacquers as have already beendeposited, and also to hold in dispersion such deterioration anddegradation products as would tend to deposit from conventional oilswith resultant fouling of engine parts. Antioxidant action is notnecessary to secure this effect and some of the most active detergentsare powerful oxidation promoters. However, not all metallic salts may beemployed in improving lubrication in this regard and even among thoseconsidered in the prior art as relatively satisfac tory, many possessthe disadvantage of exerting a corrosive effect on engine parts,particularly on engine bearings of the copper-lead and cadmium-silvertype. It is a feature of the present invention that this disadvantage isobviated. In other words, this invention is directed to the preparationof a lubricant which will maintain superior engine cleanliness and whichwill be generally suitable for a variety of engines.

The non-corrosiveness to hearing alloys of the metallic salts ofdithiocarbamic acids to which this invention relates is attributed tothe peculiar sulfur linkage involved in the molecule. This sulfurappears to exert a pacifying and protecting action upon the alloy whichprevents it from being attacked. The action is sumciently marked thatthe attack on bearing alloys by ordinarily corrosive materials, such ascarboxylic acids and soaps, may be prevented. It isadvantageous,therefore, to add a metallic dithiocarbamate to lubricatingcompositions which are either corrosive per se or become corrosive inuse, and to prepare in this manner improved lubricating compositions.

It is important also to observe that the prevention of engine foulinginvolves a detergent and dispersing action which is not found, to anygreat degree, in mineral oils per se. Furthermore, this detergentactivity is not imparted to mineral oils by any known refining method.In other words, the metallic agents contemplated in this inventionimpart to the oil blends properties seemingly not obtainable by choiceof either crude or refining technique. The metallic agents employed inthis invention are not to be considered therefore as substitutes for anyconventional refining treatment in the preparation of superiorlubricants, but as the means of imparting to mineral lubricating oilsproperties inherently lacking in the mineral oils per se.

Specifically, the mineral lubricating stocks employed in this inventionmay be any type of a mineral oil distillate or residue consistent withthe service to which the compounded lubricant is to be adapted. It isusual to prepare Diesel lubricants from non-waxy oils or naphthenic basetype oils because such oils produce a softer form of carbon which hasless tendency to scratch engine parts and does not cause ring stickingto the same extent as paraflinic oils. However, since the metalcompounds of this invention reduce the ring sticking tendency of oils,it is possible to employ even highly paraflinic oils for service wherethey would normally cause excessive ring sticking, if a proper metalliccompound is incorporated in the lubricant. The oil should possess suchflash point and viscosity characteristics as are normally consideredrequisite for the service contemplated, since the metal compounds havelittle effect upon these properties. The base oils employed may berefined by any of the conventional methods such as acid and alkalitreating, clay percolation and contacting, and by solvent extractionwith such solvents as sulfur dioxide, phenol and the like. Hydrogenatedoils as well as synthetic oils prepared, for example, by thecondensation of olefins or the reaction of carbon oxides with hydrogenmay be employed. The oils chosen will usually range in viscosity fromabout 40 to 100 seconds Saybolt at 210 F. and of this range, the mostfrequent need is for oils having a viscosity between 50 and 80 secondsSaybolt at 210 F.

The dithiocarbamate compounds added to these mineral oils have in theirmolecular structure one or more dithiocarbamate groups which may berepresented by the formula in which N, C and S have the usualsignificance as representing atoms of nitrogen, carbon and sulfur, R1and R2 representing hydrogen or organic groupings similar or dissimilarin nature, and present in the molecule so that the sum R1+R2 contains atleast eight carbon atoms in alkyl groups, and the structuralrelationship indicated by the relative positions and linkages of therespective atoms in the formula. The organic groupings represented by R1and R2 may be alkyl, aryl, alkylaryl, mixture of alkyl and aryl,cycloalkyl and heterocyclic groupings. These groupings may containinorganic substituents, such as sulfur, oxygen, phosphorus and nitrogen,when special properties are sought. Particularly important to the properfunctioning of these compounds is that they possess adequate solubilityin the mineral base stock and for'this reason it is generally requiredthat the combined R1 and R2 groups, when wholly organic, contain a totalof at least 8 carbon atoms in alkyl groups. Considerable improvement inthis regard is effected by increasing the number of carbon atoms inalkyl groups to 10, 12 and 16 preferably.

The dithiocarbamates which have been found to be especially satisfactoryare the salts of the polyvalent metals and of these the derivatives ofnickel, cobalt, magnesium, barium and calcium are worthy of specialmention. The various metallic derivatives are not equivalents in theireffects since the activities of the various compounds are determined toan appreciable extent by the nature of the particular metallic atompresent. A relation is noticeable between the eflects of the metallicderivatives of closely related elements, such as the elements of thesecond group of the periodic system of classification of the elements,namely, of calcium, magnesium and barium, and of the metals of theironsubgroup of the eighth group of the periodic system, especiallythose of nickel and cobalt. In general the magnesium, calcium and bariumcompounds are the better dispersers of sludge but are the morediil'icult to obtain in an adequately oil soluble form. Consequently,there are instances in which, despite their lesser effectiveness, it ispreferable to use the more soluble nickel and cobalt compounds. No hardand fast rule can be set up in this connection since the nature of themineral base stocks and the type of service contemplated are importantmodifying influences.

The derivatives of other metals such as chromium, tin, lead, zinc andaluminum are also of some interest in this connection but are generallyinferior to those mentioned in the preceding paragraph. The alkali metalsalts are of some value but are generally too difficult to get into oilsolution in the quantities required to warrant much consideration. Mixedmetal dithiocarbamates may be advantageously employed in many cases.Such mixtures may be merely the physical mixture of the differentmetallic dithiocarbonate compounds or different dithiocarbamate radicalsattached to the same polyvalent metal atom.

In addition to the inclusion in the thiocarbamic acid radical of organicgroups having a sufficient number of carbon atoms in alkyl groups toinsure the requisite oil solubility, the choice of a metal which is nottoo diiiicult to solubilize, and the choice of a mineral oil base ofhigh solvency, the incorporation of the metallic salt in the oil as astable addition may be assisted by the use of certain compounds whichserve as coupling agents. To some extent, these make possible the use ofcombinations which would otherwise separate in storage or in service.The coupling agents should be solvents for both the oil and the metalsalt, they should be sufliciently high-boiling as not to evaporatequickly in theengine at service temperature and they should exert nodeleterious influence upon engine performance. Esters, ketones, andother stable oxygen-containing materials and their halogenatedderivatives, halogenated hydrocarbons, and similar materials may be usedfor coupling, providing they possess a boiling point of at least 300 F.and preferably of 400 F. or higher. The amounts in which these compoundsare employed is usually between 0.5% and 1.0% by weight of the mineraloil base.

Particularly useful as coupling agents are the higher saturatedaliphatic alcohols: octyl, lauryl, cetyl, stearyl; and the correspondingoleflnic, branched-chain, cyclic and aromatic alcohols.

The optimum results are obtained by the use of cetyl and higheralcohols. The eifect is seemingly not merely one of solubilizing but thealcohol appears to enter into a loose molecular arrangement with themetal salt to provide particularly enhanced performance in engineservice.

The compositions may also include other types of compounds to conveyand/or enhance other desirable properties of the blended lubricants.Such compounds may be added for purposes of improving the viscosity,lowering the pour point or improving the color and cast characteristics.The additional use of such materials is within the scope of theinvention since these materials are added as accessories and are not ofthe nature of essential constituents so .far as the present invention isconcerned.

The amounts in which the dithiocarhamate compounds are added depend uponthe expected uses of the compounded lubricants and the particularcompound employed. In general, the dithiocarbamates are employed inproportions between 0.2% and by weight of the oil and of this rangeparticularly effective action has been noted when using amounts between0.25% and 1.0%. Quantities of thiocarbamates below 0.20% also affect theperformance of oils markedly in laboratory tests, but for improving thedetergent properties of crankcase lubricating oils, such amounts are oflimited value. Conversely, the concentrations of 0.25% or over, andparticularly of 1% or thereabout, provide compositions valuable forcleaning out already fouled engines. The fouled engine may be operatedon such a detergent oil for 5 minutes to one hour, and then flushed,though far superior results are obtained if the operation is continuedfor several days to obtain the full benefit of the detergent. Thedetergent oil should then be drawn from the crankcase and it dischargeswith it, much of the material which had been deposited in the fouledengine. When the metallic derivatives, especially those of lead, areadded in amounts of 5-10%, extreme pressure characteristics are impartedto the lubricating compositions. In all cases, the amount and the natureof the additives are adjusted so as to efiect only slight change influidity of the oil base.

The preparation of metallic dithiocarbamate compounds is illustrated bythe preparation of nickel dicyclo-hexyl dithiocarbamate. 362 grams (2mols) of dicyclohexyl amine, 152 grams (2 mols) of carbon disulfide, 83grams (about 2 mols) caustic soda and 400 cc. of water were mixed in atwo-liter flask. The reaction which occurred was very slightlynoticeable. About 200 cc. of acetone were added, and as a result ahomogeneous mixture was formed and the reaction immediately became morepronounced with the evolution of heat. The mixture was allowed to standfor about 45 minutes, and upon cooling the dithiocarbamate compoundcrystallized out. Due to the difiiculties in filtering, the product wasallowed to dry in the air. The yield of the sodium dicyclohexyldithiocarbamate was 580 grams of a light yellow crystalline product,theoretical yield being 582 grams. 291 grams (1 mol) of the aboveproduct was then dissolved in ethyl alcohol and 0.5 mol of crystallinenickel chloride (NiCl2.6H2O) added. The nickel dicyclohexyldithiocarbamate crystallized out. The material was dissolved inchloroform, and from the chloroform solution the nickel salt wasobtained by evaporation. 200 grams of the nickel dicyclohexyldithiocarbamate was recovered.

Another example of preparation of a metallic derivative of adisubstituted dithiocarbamate compound is the preparation of nickeldi-n-butyl dithiocarbamate (molecular weight 466.7) This compound wasprepared by mixing 68.1 grams of sodium di-n-butyl dithiocarbamate (0.3mol), prepared similarly to the sodium dicyclohexyl dithiocarbamateabove, in 200 cc. of water, to 45 grams (0.15 molecules) of nickelnitrate dissolved in 100 cc. of water. A precipitate of the nickeldl-n-butyl dithiocarbamate was formed which was separated, washed withwater and then with ethyl alcohol.

The product obtained was dissolved in a solvent extracted high viscosityindex lubricating oil of S. A. E. 40 characteristics in the amount of0.25% and was run for 14 hours in a single cylinder 0. F. R. gasolineengine operated at 1200 R. P. M. with a cooling jacket temperature of390 F. At the conclusion of the run,.the engine was dismantled and theengine parts, especially the piston, were carefully examined. Each partof the piston was given a demerit rating depending upon its condition:wear, cleanliness, presence of gum and/or carbonaceous deposits beingevaluated. The data were tabulated and by a correlation in which therelative importance of each demerit was considered, the overall ratingof the engine condition was obtained. The lowest demerit rating is best.In comparison with the uncompounded oil the following data wereobtained.

It is apparent that the engine condition was materially benefited inevery respect by the presence of the additive. Ring sticking wascompletely eliminated, deposition of varnish on the piston skirt wasstopped in its entirety, and the accumulation of carbon on the pistonunderside was retarded materially.

The above description and illustrative examples of the preparation andapplication of the compositions of the invention are presented forpurposes of explanation, but not of limitation, of the invention.Modifications and variations can be made therein without exceeding thescope of the invention. It is intended to claim broadly all the noveltyinherent in the invention and to be limited only by the following claimsor their equivalents.

What is claimed is:

1. A lubricating composition comprising a mineral lubricating oil and adithiocarbamate compound of formula in which R1 and R2 are organicgroupings of which R1+R2 contains at least eight carbon atoms in alkylgroups and M is a metal selected from the class consisting of alkalineearth metals and metals of the iron sub-group of the periodic system.

2. A lubricating composition comprising a mineral lubricating oil, adithiocarbamate compound of formula in which R1 and R2 are organicgroupings of which R1+Rz contains at least eight carbon atoms in alkylgroups and M is a metal selected from the class consisting of alkalineearth metals and metals of the iron sub-group of the periodic system,and a coupling agent.

3. A lubricating composition according to claim 2 in which the couplingagent is a higher alcohol.

4. A lubricating composition comprising a mineral lubricating oil andfrom 0.2% to 5%'ot an oil soluble salt of a dithiocarbamic acid and ametal of the iron sub-group of the eighth group of the periodic system.

5. A lubricating composition comprising a mineral lubricating oil andfrom 0.2% to 5.0% of an oil soluble salt of a dithiocarbamic acid and analkaline earth metal.

6. A lubricating composition comprising a mineral lubricating oil andfrom 0.2% to 5.0% of an oil soluble nickel dithiocarbamate.

7. A lubricating composition comprising a mineral lubricating oil andfrom 0.2% to 5.0% of nickel di-n-butyl dithiocarbamate.

8. A lubricating composition comprising a mineral lubricating oil and0.25% of nickel din-butyl dithiocarbamate.

9. A lubricating composition comprising a mineral lubricating oil andfrom 0.2% to 5% of a calcium salt of a dithiocarbamic acid.

10. A lubricating composition comprising a mineral lubricating oil andirom 0.2% to 5.0% 01 a barium salt of a dithiocarbamic acid.

11. The method of cleansing and lubricating automotive engines whichconsists in charging to said engines a lubricant comprising a mineralhydrocarbon oil and having incorporated therein a derivative of adithiocarbamic acid and a metal selected from the class consisting ofalkaline earth metals and metals ot the iron subgroup oi. the periodicsystem in amount and potency suilicient to obviate the formation 01'varnish and sludge deposits and to remove any such deposits alreadypresent.

12. Method of lubricating engines with a composition according to claim5 in which the dithlocarbamate compound is a derivative oi a dialkyldithiocarbamic acid.

13. Method of lubricating automotive engines with a compositionaccording to claim 4 in which the dithiocarbamate compound is the nickelsalt of di-n-butyl dithiocarbamic acid.

GEORGE L. MATHESON.

